Diagnosis of serious medical conditions has been greatly facilitated by use of medical monitoring devices which can be attached to living bodies through electrodes and which generate graphical representations, or traces, of the electrical signals generated by the body or by specific organs within the body. Such traces are characteristic of the physiological state of the living body or of the specific organ being studied, and they reveal important information to the physician or veterinarian regarding a patient's normal or abnormal medical condition in a non-invasive manner. Many kinds of traces are currently in use, for example, electrocardiograms, electroencephalograms, fetal monitoring devices, and the like.
Generally, these electrical monitoring devices function by physical attachment of an electrode to the skin of the patient, often in the vicinity of the organ to be studied. In the context of the invention, an electrode is an electrical conductor, such as a wire or lead used to establish electrical contact with a non-metallic portion of a circuit, for example, the skin of the patient. For use with electrical monitoring devices, an end of the wire or lead forming a conventional electrode may be releasably attached to an electrode coupling assembly, where the electrical coupling assembly includes an adhesive end which is attached to the patient, in a manner capturing an electrically conductive gel against the skin of the patient. The assembly further includes one portion, typically the male portion, of an electrical connector which is in direct electrical contact with the gel. The other portion of the connector is attached to the end of the electrode-to-be-attached. With this configuration, conductive attachment to the skin is effected by the electrically conductive gel. The wire of the electrode is releasably coupled to the gel through the connector portions, and thus to the monitoring device at the other end of the wire, creating an electrical circuit path from the skin through gel through the connector portions and through the wire to a monitoring device. The trace is generated by the monitoring device, typically in response to sensed conductivity between the skin at the gel-skin interface and another electrode connection to the patient.
Traces generated in this manner are representative of such electrical signals, but also include noise components, making it difficult to measure or monitor the desired parameter. Such noise may be due to a number of factors and sources, but a primary source is the patient's movements. Such movements typically disturb the electrical connections in the electrode coupling assembly described above. In particular, the attachment of the electrode via its connector to the electrical coupling assembly places a load force (due to weight of the electrode wire itself, for example) on the connector portion of the electrode coupling assembly, which is coupled to the gel. As the patient moves, causing reorientation of the coupling assembly, the load force on the gel varies accordingly. In response, the electrical conductivity of the gel between the connector and skin varies, resulting in a noise component added to the monitored electrical signal. Also, noise is generated by changes in electrical conductivity resulting from relative motion of the portions of the connector. For example, patients may pull on the electrode wire or scratch at the site of the adhesive attachment to the skin. If a small monitoring device is being used, it may temporarily hang from the wire. All of these events may cause strain on the connecting wire and resulting electrical noise. Noise interference created by the patient's movements can be especially problematic when the patient is ambulatory, for example, when the monitoring device is attached for an extended period of time to obtain a trace over time of an organ's electrical activity and the patient is allowed to move about or to go home. Strain on the electrode wire is common in traces of ambulatory patients. Traces generated for veterinary purposes are particularly subject to noise interference caused by patient movement.
The problem of spurious signals generated by relative movement between the connector portions has been recognized in the past. Medical practitioners have attempted to minimize movement of the connector portions by taping the end of the electrode near its connector portion to the patient, providing a measure of strain relief. However, this limits the ease of use since removal is difficult, and additionally, the adhesive tape itself can be a source of discomfort and inconvenience to the patient.
There have been prior art attempts at minimizing such noise, for example as disclosed in U.S. Pat. No. 4,757,817. In that patent, a single electrode connection pad is disclosed which includes both an aperture for application of the conductive gel and a connector portion for receiving an electrode connector and wire extending from a monitoring device. In U.S. Pat. No. 4,757,817, the pad is slit to establish an adhesive-backed flap used to secure the electrode wire to the pad, establishing a measure of strain relief. However, the slitted pad of U.S. Pat. No. 4,757,817 is a unitary structure and does not provide any physical separation between the strain relief feature point and the gel-bearing electrode-to-skin coupling.
U.S. Pat. No. 4,209,020 discloses a fetal monitoring electrode assembly with a single contact pad which establishes electrical contact with the mother's skin through an aperture under a connector element and which is directly attached to the monitoring device. Separate electrodes are attached to the fetus. The contact pad of U.S. Pat. No. 4,209,020 is affixed to the mother's thigh, thus purportedly minimizing movement of the fetal electrodes relative to the monitoring device. However, with a single pad housing both the electrode-to-skin coupling (gel) and the connection to the electrode wire, movement in either the fetus or the wire changes the shape of the gel, resulting in noise.
U.S. Pat. No. 4,503,860 discloses an adhesively attached pad in a serial arrangement with a connector arranged for releasable coupling to a primary electrode coupling device. That pad functions to stabilize an electrode in the vicinity of the measuring point and to relieve strain on the lead at its point of connection to the electrode proper. The anchor means of U.S. Pat. No. 4,503,860 is located a short distance away from the electrode. However, the anchor pad is integrated with the electrode lead and connector, so that each time the electrode is to be connected or disconnected, the primary electrical coupling device must be disturbed, resulting in a change in position of that coupling device and introducing measurement error.
In the electrode of U.S. Pat. No. 3,977,392, an aperture containing the conductive gel is separated from the male snap on a single adhesive pad by a flexible conductor which is purported to prevent physical contact between the conductive gel and the male snap. The only flexible conductor disclosed in U.S. Pat. No. 3,977,392 is a thin silver foil strip about 11/4 inches long and 3/16 inch wide.
It is an object of the invention to provide an improved strain relief coupling assembly for an electrode.
Another object is to provide a strain relief coupling assembly which permits releasable attachment of an electrode with minimal disturbance to a primary electrical signal coupler.
Another object of the invention is to provide relief of strain caused by patient movements on a wire connecting a monitoring device to an electrode.